1. Field of the Invention
The present invention relates to the preparation of silver halide photographic light-sensitive materials, and more particularly, to a novel method for preventing the degradation of a hydrophilic colloid which is employed as a binder for silver halide photographic materials.
2. Description of the Prior Art
In general, silver halide photographic light-sensitive materials comprise a support having thereon one or more light-sensitive silver halide emulsion layers and, depending upon necessity, having further thereon layers such as a subbing layer, an intermediate layer, a filter layer, an antihalation layer, a protective layer, etc. Known hydrophilic colloids which are employed as binders for these photographic layers include proteins such as gelatin, albumin, casein, etc.; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, etc.; saccharide derivatives such as agar, sodium alginate, starch derivatives, etc.; synthetic hydrophilic colloids such as polyvinyl alcohol, poly-N-vinylpyrrolidone, polyacrylic copolymers, etc. Of these, gelatin is most generally employed. Further, the gelatin can be replaced partially or completely by gelatin derivatives, i.e., those obtained by treating the amino groups, imino groups, hydroxy groups or carboxyl groups which are present as functional groups in the gelatin, with compounds capable of reacting with these groups, or by graft polymers obtained by grafting the molecular chains of high molecular weight substances, and the like, onto the gelatin molecule. Alternatively, use of two or more kinds of hydrophilic colloids, e.g., the use of a mixture of gelatin and other high molecular weight substances, in combination is also known.
On the other hand, it is known that these hydrophilic colloids employed for silver halide photographic materials deteriorate, decay or are decomposed by the action of bacteria, molds, yeasts, etc. For example, upon preparation of photographic materials, if these hydrophilic colloids deteriorate or are decomposed, the viscosity of the coating solution and the physical strength of the coated layer are reduced, and, in addition thereto, localized decomposition of these hydrophilic colloids occurs so that uniformity of the coated layers is lost, or the decomposition products of hydrophilic colloids adversely affect the photographic properties in certain instances.
In order to prevent this deterioration or decomposition (hereinafter the term "degradation" will be used to describe collectively all of these deleterious changes which occur) of hydrophilic colloids employed for photographic materials due to bacteria, molds, yeasts, etc., preservatives or antifungal agents have been incorporated into solutions containing the hydrophilic colloids described above at some stage during the preparation of the photographic materials.
Agents which can be used, in general, as preservatives or antifungal materials include, for example, aromatic hydroxy compounds such as phenol, thymol, trichlorophenol, tetrachlorophenol, pentachlorophenol, cresol, p-chloro-m-cresol, o-phenylphenol, benzylphenol, 2-benzyl-4-chlorophenol, chlorophen, dichlorophen, bromochlorophen, 2,2'-dihydroxy-5,5'-dichlorodiphenyl monosulfide, 2,4,4'-trichloro-2'-hydroxydiphenyl ether, 3,4,5-tribromosalicyl anilide, or the salts thereof; compounds containing a carbonyl group such as formaldehyde, paraformaldehyde, chloroacetaldehyde, glutaraldehyde, chloroacetamide, methylol chloroacetamide; carboxylic acids or esters thereof such as benzoic acid, monobromoacetic acid esters, p-hydroxybenzoic acid esters, sorbic acid; amines such as hexamethylenetetramine, alkylguanidines, nitromethylbenzylethylenediamine; disulfides such as tetramethylthiuram disulfide; nitrogen-containing heterocyclic compounds such as 2-mercaptobenzothiazole, 2-(4-thiazolyl)benzimidazole, 2-methoxycarbonylaminobenzimidazole; organic mercury compounds such as mercury phenylacetate, mercury phenylpropionate, mercury phenyloleate; antibiotics such as neomycin, kanamycin, polymycin, streptomycin, furamycin, and the like. Some of these compounds are also known to be suitable for use in photography. However, the effects of these agents are exhibited only when a large amount of these agents is added to hydrophilic colloids and, in most cases, these agents are hazardous to humans, effective only against certain bacteria, are harmful photographically, or mutually interact with other photographic additives. For example, phenols such as phenol and thymol which are very often employed do not provide sufficient preservation effects unless they are present in the hydrophilic colloids in an amount of about 2 wt% or more. In addition, phenols provide less preservation and antifungal effects against molds or yeasts and are strongly toxic to humans, even though they are effective against bacteria. Further, aldehydes such as formaldehyde are effective against bacteria but only slightly effective against molds and are harmful to humans and further fog in silver halide photographic light-sensitive materials tends to occur when they are used. Further, heterocyclic compounds such as benzothiazole result in deleterious photographic effects such as desensitization in certain instances. Organic mercury compounds are only slightly effective against bacteria and are harmful to humans, although they are effective against molds. Antibiotics such as neomycin, kanamycin are ineffective against yeasts, although they are effective against bacteria.
As described above, many preservatives are known. However, these conventional preservatives are not directly usable as preservatives for photography. This is because, as is well recognized in the art, extremely delicate handling is necessary in photographic area. All photographic additives must have the following photographic properties: (1) they must not cause a reduction in sensitivity to occur, especially during storage under high temperature and high humidity, (2) they must not cause a change in gamma to occur, (3) they must not cause fog, (4) they must not adversely affect the stability of latent images formed, and (5) the processing must be smooth when they are used. For example, it is known that conventional phenol type preservatives cause desensitization under the conditions of high temperature and high humidity when the amount employed is high in order to obtain sufficient preserving activity. Neomycin also causes desensitization at high humidity and high temperature. Therefore, it has been long desired to develop all-round preservatives which do not adversely affect photographic properties.
On the other hand, uniformity of the layers of photographic light-sensitive materials and coating at a high speed are desired. As a result, it is necessary to control the viscosities of respective layers to desired values in order to enable uniform coating at high speed, particularly where two or more layers are coated simultaneously or continuously using coating techniques such as extrusion coating, curtain coating, air knife coating, or the like. In particular, where the coating is onto a support travelling at a speed of about 20 m/min or more, it is difficult to achieve uniform coating if the viscosity of the coating solution is low. In addition, where two or more layers are simultaneously coated, the relative values of the viscosities of the coating solutions for the respective layers must be adjusted so that uniform coating can be achieved.
Viscosity-increasing agents must be added to photographic coating solutions to facilitate uniform coating of the coating solution onto a support. Particularly in the past several years, the demand for high speed coating has been increasing and high speed coating on an industrial scale is achieved by increasing the viscosity of a coating solution.
Another demand is to improve the quality of a photographic element by converting photographic layers into a multilayered structure, generally composed of 6 to 20 layers. In such a case, it is essential for the viscosities of the coating solutions to be well balanced among the layers by purposely using viscosity-increasing agent. In addition, enhancement of viscosity using viscosity-increasing agents saves gelatin which is expensive since gelatin is often employed also as a viscosity-controlling agent due to the photographically inert properties of gelatin.
It is known to incorporate polymers containing acid groups such as carboxyl groups or sulfonyl groups into coating solutions to increase the viscosity of coating solutions for photographic layers.
For example, a method for increasing the viscosity by incorporating a compound of the general formulas: ##STR2## wherein R.sub.0 represents an aliphatic or aromatic hydrocarbon residue and S represents a sulfonic acid group, a salt thereof or a derivative thereof, --SO.sub.3 R'.sub.1, --SO.sub.3 X, or --SO.sub.2 NR'.sub.1 R'.sub.2, wherein R'.sub.1 and R'.sub.2, each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group; and X represents an ammonium group, a potassium atom, a sodium atom or another alkali metal atom; into a solution containing gelatin is described in Japanese Patent Publication No. 3582/1960.
Further, Photographic Science and Engineering, Vol. 14, pages 178 to 183 (1970) discloses that ammonium salts of copolymers of maleic anhydride and methyl vinyl ether, polystyrene sodium sulfonate, polyvinyl ammonium phthalate, dextran sodium sulfate, etc., can be employed as viscosity-increasing agents for gelatin and derivatives thereof. In addition, Japanese patent application (OPI) No. 45830/1972 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses that polymers or copolymers of acrylic acid, maleic acid or styrene sulfonic acid, or cellulose derivatives containing acid groups (e.g., carboxymethyl cellulose, cellulose sulfate) can be incorporated into a gelatin intermediate layer.
As stated above, phenol preservatives such as phenol or thymol which are generally employed as preservatives for hydrophilic colloids for photography have the disadvantage that the preservation effect is not obtained unless a large amount thereof is added to hydrophilic colloids, due to their poor preservation effect. For instance, in the case of a photographic coating solution using gelatin as a hydrophilic colloid, a sufficient preservation effect is not obtained unless the phenols are employed in an amount of 2 wt% or more based on the gelatin (solids content). As such, where a large amount of phenol is incorporated in photographic coating solutions, there is the disadvantage that it is difficult to produce a uniformly coated layer since gelatin tends to aggregate in the coating solution. Where anionic polymers for increasing the viscosity are incorporated into photographic coating solutions containing a phenol, a large amount of a viscosity-increasing agent must be added because the viscosity-increasing effect is prevented by the phenol.
A photographic hydrophilic colloid solution, e.g., an aqueous gelatin solution, necessarily has a cationic pH. In order to prevent degradation of such a photographic solution, preserving activity can be most effectively achieved by causing an ionic interaction of the resulting cationic phase with an anionic compound. In addition, bacteria themselves do not grow in a low pH range so that the use of an acidic compound is dictated as a preserving agent.
Conventional preservatives severely restricted as to functional requirements are extremely pH-dependent. For example, benzoic acid, sorbic acid and benzyl alcohol, which are most typical preservatives for a gelatin solution, exhibit their preserving activity only up to a neutral pH at the highest.
The most serious problem is, as stated above, the undesired reduction in viscosity of the system when such conventional preservatives and anionic polymer viscosity-increasing agents are used in combination.
As a result, it has been desired to develop preservatives for photographic hydrophilic colloids which exhibit a variety of preservation effects and which can be used in a small amount, i.e., which exhibit marked anti-degradation and antifungal effects against bacteria, yeasts, molds, etc. In addition, it has been desired to develop preservatives for photographic hydrophilic colloids which do not adversely affect the viscosity-increasing effects of viscosity-increasing agents.